Double-loop Microtrap for Ultracold Atoms

A microtrap consisting of two concentric circular loops having radii of 300 and 660 $\mu$m, respectively, is demonstrated. The microtrap is formed using the magnetic field generated by the current passing through the double-loop wire pattern superposing a small external bias magnetic field perpendicular to the wire pattern plane. The double-loop wire pattern is fabricated on an atom chip device. The maximum three dimensional trap depth exceeds 1 mK when using an atom chip current of 2.6 Amps. The trap position below the atom chip surface can be adjusted over a distance of 100 microns by varying the bias field. Experimentally, more than $10^5$ $^{87}$Rb atoms were loaded into the microtrap from a quadrupole magnetic trap and remained trapped for several hundred milliseconds which was limited by the background pressure. The loading of a linear array of three microtraps is also demonstrated. The trap dimensions are readily scaled to micrometer size, which is of interest for creating a one and two dimensional array of neutral atom traps on a single atom chip.